It can be concerning to not detect a fetal heartbeat at 7 weeks, especially if hCG levels are rising. While a visible heartbeat is typically detected by this stage, there can be variations in development among pregnancies. It's possible that the gestational age was initially miscalculated or that the embryo is developing slower than expected. In some cases, a follow-up ultrasound may reveal a heartbeat later on. However, if subsequent ultrasounds continue to show no heartbeat or signs of growth, it may indicate an early pregnancy loss or other complications. It's important to consult with your healthcare provider for further evaluation and guidance based on your specific situation.